Embodiments according to the invention relate to a two-point polar modulator, i.e. a polar modulator having a two-point phase-locked loop. Some embodiments relate to a two-point modulator which may be used in mobile radio telephones which utilize modulation methods with a non-constant envelope for increasing the data rate, e.g. according to the mobile radio standard GSM-EDGE (GSM=global system for mobile communication; EDGE=enhanced data rate for GSM evolution).
With the rapidly progressing development on the mobile radio market, the development of power-efficient wireless transmit/receive architectures has become an important point for the design of portable mobile devices. Mobile radio telephones of the next generation which utilize the GSM-EDGE standard for example use modulation methods with a non-constant envelope for achieving higher data rates. The manufacturers of cellular mobile radio telephones in some case request similar talk and standby times for the GSM standard of the next generation. In order to fulfill this request, or at least to make a contribution to the same, power-efficient radio transmission architectures are required.
In the latest generation of transceivers, a polar modulator concept is being used more and more the advantage of which is its robustness against parasitic couplings of the power amplifier output signal into the phase-locked loop of the polar modulator. This concept has already proved successful for GSM-GPRS systems (GPRS=general packet radio service). For EDGE systems, however, the coupling of the output signal into the voltage-controlled oscillator (VCO) of the phase-locked loop (PLL) sometimes causes the generation of unwanted AM-FM signal components (AM=amplitude modulation, FM=frequency modulation) which become noticeable with an interference of the FM signal at the output of the VCO. The unwanted AM/FM signal components lead to a significant deterioration of the modulation spectrum and increase error performance. Partially, by this the tolerance mask of the frequency spectrum may be violated with GSM-EDGE modulations.
In order to reduce the influence of the parasitic coupling path of the output signal of the power output stage with GSM-EDGE modulation methods, suitable measures at the polar modulator are desired which prevent such a coupling of the output signal, and compensate or at least suppress the same.